Electroluminescence (EL) elements utilizing a substance which emits light by itself through an EL phenomenon when a voltage is applied thereto are known as a type of light emitting element which forms a display apparatus such as a display device and an illumination apparatus. The EL element is a light emitting element of thin film shape in which a light emission layer made from an organic material or an inorganic material is formed between an upper electrode and a lower electrode, and has a structure in which light emission is caused by applying a voltage to the light emission layer with the upper electrode and the lower electrode.
In recent years, development work has been underway on light emitting elements having a resonator structure (a so-called microcavity structure) in which one of the upper electrode and the lower electrode is formed of a total reflection mirror and the other is formed of a semi-transmitting mirror allowing transmission of some of wavelengths, thereby resonating light emitted by the light emission layer (see, for example, Patent Documents 1 and 2).
Patent Document 1 has disclosed a light emitting element in which the peak wavelength of an inner light emission spectrum is shifted from the peak wavelength of a multiple interference spectrum in a resonance portion to reduce dependence of white color on viewing angle. The reduction of the dependence of white color on viewing angle is realized by shifting the peak wavelength of the multiple interference spectrum of a red color (R) toward longer wavelengths (+10 nm), the peak wavelength of the multiple interference spectrum of a green color (G) toward longer wavelengths (+4 nm), and the peak wavelength of the multiple interference spectrum of a blue color (B) toward shorter wavelengths (−10 nm).
Patent Document 2 has disclosed a light emitting element in which the peak wavelength of an inner light emission spectrum is shifted from the peak wavelength of a multiple interference spectrum in a resonance portion to reduce dependence on viewing angle. However, unlike Patent Document 1, the peak wavelengths of the multiple interference spectra of a red color (R) and a blue color (B) are matched to the peak wavelength of the inner light emission spectrum.
The techniques disclosed in Patent Documents 1 and 2 may be effective in display apparatuses, for example a large display, which require the characteristics of wide viewing angle. However, unacceptable nonuniformity of luminance in a front direction may occur in small displays for personal use, for example mobile terminals, personal computers, and car navigation systems.
Specifically, when the resonator structure is used, its filter characteristics and high directivity of light emission output increase the luminance in the front direction. Display apparatuses which do not require the characteristics of wide viewing angle, for example ones for personal use, take advantage of the directivity and thus need reduced nonuniformity of luminance in the front direction as compared with televisions and the like which require a wide viewing angle. However, the thin-film light emitting element of the resonator structure has filter characteristics which are sensitive to an intermirror distance (resonator optical path length), and if nonuniformity occurs in the resonator optical path length due to manufacture errors during the manufacture process, color coordinates (color purity) and luminance variations in the front direction may be unacceptable.